Method for reducing power consumption of terminal in mobile communication system using multi-carrier structure

ABSTRACT

A method for reducing power consumption of a terminal that communicates with a base station in a mobile communication system using a multi-carrier structure composed of a primary component carrier and at least one secondary component carrier comprises: receiving a discontinuous reception (DRX) parameter group for multi carriers from the base station; and setting the multi carriers to the same parameter value, by using the received parameter group. The method for reducing power consumption of the terminal further comprises: performing a downlink control channel receive operation on each carrier according to a DRX cycle. As the base station in the mobile communication system using the multi-carrier structure simplifies the DRX process for reducing power consumption of a terminal by reducing signaling load for the multi-carrier control of the terminal, it becomes possible to reduce power consumption of the terminal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/541,203, filed on Aug. 15, 2019 (now pending), which is acontinuation of U.S. application Ser. No. 15/659,339, filed on Jul. 25,2017 (U.S. Pat. No. 10,405,277), which is a continuation of U.S.application Ser. No. 14/923,468, filed on Oct. 27, 2015 (now U.S. Pat.No. 9,717,053), which is a continuation of U.S. application Ser. No.13/383,455, filed on Jan. 11, 2012 (now U.S. Pat. No. 9,191,179), whichis a 371 national phase entry of International Application NumberPCT/KR2010/006730, filed on Oct. 1, 2010, which claims priority to, andthe benefit of, Korean Application Nos. 10-2010-0001516, filed on Jan.8, 2010 and 10-2009-0093895, filed on Oct. 1, 2009. The contents of theaforementioned applications are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

Example embodiments of the present invention relate in general to amethod of reducing power consumption of a terminal in a long termevolution (LTE) system, which is under standardization by 3rd GenerationPartnership Project (3GPP), performing communication between a basestation and the terminal, and more specifically to a method for a basestation to efficiently control a discontinuous reception (DRX) operationof a terminal in a mobile communication system using multiple carriers.

BACKGROUND ART

3GPP, a mobile communication standardization organization, developed theLTE system standard to develop a next-generation mobile communicationstandard. Also, to meet International Mobile Telecommunication(IMT)-advanced requirements suggested by International TelecommunicationUnion Radio communications (ITU-R), an LTE-advanced system standard,which is an extended LTE standard, is under development.

The LTE standard supports a maximum wireless bandwidth of 20 MHz formobile communication, and the LTE-advanced standard uses carrieraggregation technology to support a maximum bandwidth of 100 MHz. Thus,the bandwidth of 100 MHz is divided into component carriers (CCs) havinga maximum bandwidth of 20 MHz, and a base station and a terminal cancommunicate with each other using a plurality of CCs at the same time.

Since a terminal operating in a carrier aggregation structure receives aplurality of wireless channels in a wideband, power consumptionincreases. To solve this problem, a control procedure for minimizingpower consumption in a multi-carrier environment is needed.

DISCLOSURE Technical Problem

Accordingly, in order to substantially obviate one or more problems dueto limitations and disadvantages of the related art, an object of thepresent invention provide a method of reducing power consumption of aterminal communicating with a base station in a mobile communicationsystem using multiple carriers for reducing power consumption ofterminals.

One aspect of the present invention provides a method of reducing powerconsumption of a terminal communicating with a base station usingmultiple carriers includes: receiving one discontinuous reception (DRX)parameter group for multiple carriers from the base station; receiving avalue of the one parameter group, and setting the multiple carriers tothe same parameter value; and performing an operation of receiving adownlink (DL) control channel for each of the carriers according to aDRX cycle. Also, the performing the operation of receiving the DLcontrol channel for each of the carriers according to the DRX cycle mayinclude performing, at all the carriers, the operation of receiving theDL control channel in the same way. The performing the operation ofreceiving the DL control channel for each of the carriers according tothe DRX cycle may include: when the DL control channel is received on acarrier of the terminal, interpreting the received control channel todemodulate the corresponding data channel; and continuously performingan on-duration operation until a new control channel is received in anext subframe time, and then switching to a sleep operation when a newcontrol channel is not received during a time of an inactivity timer.The performing the operation of receiving the DL control channel foreach of the carriers according to the DRX cycle may include, when acarrier indicator (CI) is included in the received control channel,receiving a data channel of a carrier corresponding to a carrier numberindicated by the CI and demodulating data. The terminal may receive amessage instructing the terminal to switch a DRX operation cycle foranother carrier from a short DRX cycle to a long DRX cycle, a messageinstructing the terminal to switch the DRX operation cycle for the othercarrier from the long DRX cycle to the short DRX cycle, a messageinstructing the terminal to stop an operation of transmitting andreceiving the other carrier, and a message instructing the terminal tostart the operation of transmitting and receiving the other carrier fromthe base station. The performing the operation of receiving the DLcontrol channel for each of the carriers according to the DRX cycle mayinclude, when the terminal receives a physical downlink control channel(PDCCH) in a long DRX period state, demodulating the PDCCH or a physicaldownlink shared channel (PDSCH), and when it is not necessary to switchto a short DRX period state, staying in the long DRX period state. Theperforming the operation of receiving the DL control channel for each ofthe carriers according to the DRX cycle may include: when the terminalreceives the PDCCH in the long DRX period state, demodulating the PDCCHor the PDSCH to determine whether or not a type of data requirescontinuous data communication; when it is determined that the type ofdata does not require continuous data communication, staying in the longDRX period state; and when it is determined that the type of datarequires continuous data communication, switching to the short DRXperiod state. A case in which the type of data does not requirecontinuous data communication may include at least one of a case inwhich the base station allocates an uplink (UL) radio resource but thereis no data in a buffer of the terminal, a case in which the base stationrequests UL transmission to maintain UL synchronization, a case in whichthe base station requests UL transmission to search for locationinformation about the terminal, and a case in which the base stationrequests a DL channel state report.

Another aspect of the present invention provides a method of reducingpower consumption of a terminal communicating with a base station usingmultiple carriers includes: transmitting, at the base station, aconfiguration message to the terminal so that the terminal can carry outa configuration procedure of controlling a plurality of carriers; andtransmitting, at the base station, a carrier activation message to theterminal so that the terminal stands by without using a carrier, whichis instructed to be configured by the configuration message, forcommunication with the base station and then uses a carrier, which isinstructed to be activated by the carrier activation message, forcommunication with the base station when a carrier activation procedureis complete. The activation message may be transmitted through a datachannel transmitted to the terminal by the base station, and may includeat least one of an activation carrier number, a deactivation carriernumber, an activation identity, and a deactivation identity. A pluralityof the carrier activation messages may be stored in one data channeltransmitted to the terminal, and transmitted. The base station maytransmit a deactivation message to the terminal to switch the terminalto a standby state for the activated carrier. The carrier activationprocedure may be carried out for a DL carrier. The carrier activationprocedure may be carried out for a UL carrier in connection withactivation of the DL carrier. To be specific, in the UL carrieractivation procedure carried out in connection with activation of the DLcarrier, the base station may include mapping information about the ULcarrier interoperating with the DL carrier in a DL configuration messageand transmit the DL configuration message to the terminal so that the ULcarrier mapped to the DL carrier instructed to be activated is activatedand used for communication with the base station when the DL carrier isinstructed to be activated by the terminal.

Still another aspect of the present invention provides a method ofreducing power consumption of a terminal communicating with a basestation in a mobile communication system using multiple carriersincluding a primary component carrier and at least one secondarycomponent carrier includes: transmitting, at the base station, aconfiguration message to the terminal; and transmitting, at the basestation, a carrier activation message to the terminal. The configurationmessage may include carrier mapping information between UL carriersinteroperating with the DL carriers. The method may further includehaving a DL carrier indicated by the carrier activation message to beactivated. When the carrier mapping information is included in theconfiguration message and transferred to the terminal, the UL carriersmay be implicitly activated in connection with activation of the DLcarriers. DL carriers may be activated in connection with activation ofDL carriers. Different numbers of the DL carriers and the UL carriersmay be mapped to each other. When the different numbers of the DLcarriers and the UL carriers are mapped to each other, the UL carriersmay be implicitly activated in connection with activation of the DLcarriers by including the carrier mapping information in theconfiguration message and transferring the configuration message to theterminal. The configuration message may be a radio resource control(RRC) message including the number of additional secondary cells(Scells) and secondary component carrier (SCC) control information. Theactivation message may be transmitted to the terminal through a mediaaccess control (MAC) control message. The activation message may beincluded in a data channel in the MAC control message and transmitted. Aplurality of the carrier activation messages may be stored in the datachannel in the MAC control message transmitted to the terminal, andtransmitted. The MAC control message may include a control channel and adata channel, and the data channel may include a data channel header,the carrier activation message, and traffic data. The method may furtherinclude transmitting, at the base station, a carrier deactivationmessage to the terminal to switch the terminal to a standby state for acarrier indicated by the carrier activation message. The carrieractivation message may include at least one of a physical uplink controlchannel (PUCCH), which is a UL control channel, and a transmission cycleof a sounding reference symbol (SRS).

Advantageous Effects

According to example embodiments of the present invention, a basestation in a mobile communication system using multiple carriers reducessignaling for multi-carrier control of a terminal to simplify a DRXprocedure for reducing power consumption of the terminal, so that thepower consumption of the terminal can be reduced. Also, using asimplified control message, a call processing procedure of the systemcan be reduced.

DESCRIPTION OF DRAWINGS

FIG. 1 is a timing diagram illustrating a discontinuous reception (DRX)operation of a terminal in a mobile communication system.

FIG. 2 is a timing diagram illustrating a DRX operation of a mobilecommunication system having a multi-carrier structure using a carrierindicator (CI) according to example embodiments of the presentinvention.

FIG. 3 is a flowchart illustrating a process of switching a DRXoperation cycle for one or more carriers from a short DRX cycle to along DRX cycle in a downlink (DL) of a mobile communication system usingmultiple carriers according to example embodiments of the presentinvention.

FIG. 4 is a flowchart illustrating a process of switching a DRXoperation cycle for one or more carriers from a long DRX cycle to ashort DRX cycle in a DL of a mobile communication system using multiplecarriers according to other example embodiments of the presentinvention.

FIG. 5 is a flowchart illustrating a process for a base station toactivate a carrier of a terminal in a mobile communication system usingmultiple carriers.

FIG. 6 is a conceptual diagram illustrating a process for a base stationto activate a carrier of a terminal in a mobile communication systemusing multiple carriers.

FIG. 7 illustrates a structure of a carrier activation messagetransmitted to a terminal by a base station.

BEST MODE

Example embodiments of the present invention are disclosed herein.However, specific structural and functional details disclosed herein aremerely representative for purposes of describing example embodiments ofthe present invention, however, example embodiments of the presentinvention may be embodied in many alternate forms and should not beconstrued as limited to example embodiments of the present invention setforth herein.

Accordingly, while the invention is susceptible to various modificationsand alternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the particular forms disclosed, but on the contrary, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(i.e., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

The term “terminal” used herein may be referred to as a mobile station(MS), user equipment (UE), user terminal (UT), wireless terminal, accessterminal (AT), subscriber unit, subscriber station (SS), wirelessdevice, wireless communication device, wireless transmit/receive unit(WTRU), moving node, mobile, or other terms. Various example embodimentsof a terminal may include a cellular phone, a smart phone having awireless communication function, a personal digital assistant (PDA)having a wireless communication function, a wireless modem, a portablecomputer having a wireless communication function, a photographingapparatus such as a digital camera having a wireless communicationfunction, a gaming apparatus having a wireless communication function, amusic storing and playing appliance having a wireless communicationfunction, an Internet home appliance capable of wireless Internet accessand browsing, and also portable units or terminals having a combinationof such functions, but are not limited to these.

The term “base station” used herein generally denotes a fixed pointcommunicating with a terminal, and may be referred to as a Node-B,evolved Node-B (eNode-B), base transceiver system (BTS), access point,and other terms. One or more cells can be present in the coverage areaof one base station.

The term “carrier” used herein has the same meaning as a componentcarrier (CC) when carrier aggregation is applied to the carrier.

The term “primary cell (Pcell)” used herein denotes a cell that isinitially configured during connection establishment, and plays anessential role with regard to security, upper layer system information,and some lower layer functions.

The term “secondary cell (Scell)” used herein denotes a cell that isconfigured after connection establishment to merely provide additionalradio resources.

The term “serving cell” may denote a Pcell or Scell, and may be used todenote a set of one or more cells including a Pcell and all Scells.

In the case of carrier aggregation, one serving cell provides non-accessstratum (NAS) mobility information, e.g., a tracking area identity(TAI), upon radio resource control (RRC) connectionestablishment/connection re-establishment/handover, and one serving cellprovides a security input upon RRC connection re-establishment/handover.Here, the TAI denotes a tracking area for managing base stations locatedwithin a predetermined range together, and is generated as a unitmanaged by the NAS from a public land mobile network (PLMN) identitythat the tracking area belongs to and a tracking area code (TAC) of thetracking area. Such a serving cell will be defined as a Pcell below.

In the case of carrier aggregation, carriers can be classified as aprimary component carrier (PCC) and a secondary component carrier (SCC).

In a downlink (DL), a carrier corresponding to the Pcell is defined as aDL PCC, and in an uplink (UL), a carrier corresponding to the Pcell isdefined as a UL PCC.

According to a capability of a terminal, a Scell can constitute a set ofserving cells together with a Pcell. In a DL, a carrier corresponding tothe Scell is defined as a DL SCC, and in a UL, a carrier correspondingto the Scell is defined as a UL SCC.

Thus, a set of serving cells for one terminal includes one Pcell and atleast one Scell. The number of configurable serving cells can be setaccording to an aggregation capability of the terminal. The Pcell can bechanged only through a handover procedure. The Pcell is used fortransmission of a UL control channel, e.g., a physical uplink controlchannel (PUCCH). The Pcell can be distinguished from the Scell in thatthe Pcell cannot be deactivated.

Hereinafter, example embodiments of the present invention will bedescribed in detail with reference to the appended drawings. To aid inunderstanding the present invention, like numbers refer to like elementsthroughout the description of the figures, and description of the samecomponent will not be reiterated.

FIG. 1 is a timing diagram illustrating a discontinuous reception (DRX)operation of a terminal in a mobile communication system, and FIG. 2 isa timing diagram illustrating a DRX operation of a mobile communicationsystem having a multi-carrier structure using a carrier indicator (CI)according to example embodiments of the present invention.

A terminal is controlled according to an on-duration period 12 in whichthe terminal receives a DL control channel transmitted by a basestation, and a period 14 in which the terminal stops the receivingoperation and performs a sleep operation to reduce power consumption.When the base station does not transmit a control channel to theterminal while the terminal performs the on-duration operation, theterminal determines that it is not necessary to receive data andswitches to the sleep operation. A cycle in which the terminal performsthe on-duration operation is indicated by a DRX cycle 10. The DRX cycle10 is separately indicated by a long DRX 20 and a short DRX 40. The longDRX 20 can minimize power consumption because a data receiving cycle ofthe terminal is large.

A power consumption reducing operation of a terminal in a mobilecommunication system using multiple carriers is performed in parallel tocontrol the multiple carriers including one PCC and at least one SCC.Thus, the terminal controls a DRX operation according to the respectivecarriers (PCC and SCC). More specifically, a base station transmits amessage for DRX control to the terminal, and the DRX control messageincludes parameter values, such as an on-duration, a long DRX cycle, ashort DRX cycle, and an inactivity timer, for controlling the DRXoperation of the terminal. A media access control (MAC) messagegenerated in the MAC layer can be used as the DRX control message. TheMAC message can have a size of N bits (N is a natural number).

In example embodiments of the present invention, to reduce the size of acontrol message transmitted by a base station in a mobile communicationsystem using multiple carriers, the base station transmits one DRXparameter group to a terminal, and the terminal receives a value of theone parameter group and sets the multiple carriers to the same parametervalue. Thus, a plurality of DRX parameter groups required to transmitrequired parameters according to respective carriers (PCC and SCC) arenot required.

When a DRX environment is set, a terminal performs an operation ofreceiving a DL control channel for respective carriers (PCC and SCC)according to a DRX cycle. When a DL control channel is received on a CCof the terminal, the terminal performs a data channel receivingoperation. Also, the terminal continuously performs an on-durationoperation and waits for a new control channel to be received in a nextsubframe time. This operation stands by for a time corresponding to avalue of an inactivity timer, and the terminal switches to the sleepoperation when a new control channel is not received during the time ofthe inactivity timer.

In example embodiments of the present invention, to support a DRXoperation of a terminal, a base station transmits the following messagesto the terminal.

1. The base station instructs the terminal to switch a DRX operationcycle for one or more CCs from a short DRX cycle to a long DRX cycle.The long DRX instruction message includes a message identity, a carrieridentity, etc., and is generated at the MAC layer and transmitted.

2. The base station instructs the terminal to switch a DRX operationcycle for one or more CCs from a long DRX cycle to a short DRX cycle.The short DRX instruction message includes a message identity, a carrieridentity, etc., and is generated at the MAC layer and transmitted.

3. The base station instructs the terminal to stop an operation oftransmitting and receiving one or more carriers. The message isgenerated at an RRC layer and transmitted.

4. The base station instructs the terminal to start an operation oftransmitting and receiving one or more carriers. The message isgenerated at the RRC layer and transmitted.

In a mobile communication system of FIG. 2 having a multi-carrierstructure using a CI, a terminal interprets a control channel, e.g., aphysical downlink control channel (PDCCH), received on one PCC, e.g.,CC1 of FIG. 2 , to demodulate the corresponding data channel, e.g., aphysical downlink shared channel (PDSCH). When a CI is included in thereceived control channel (“PDCCH with CI” of FIG. 2 ), the terminalreceives a data channel of an SCC corresponding to a carrier numberindicated by the CI, e.g., CC2 of FIG. 2 , to demodulate data.

In this operation, a base station in the mobile communication systemhaving the multi-carrier structure transmits the following messages tothe terminal, thereby controlling DRX.

1. The base station instructs the terminal to switch a DRX operationcycle for another carrier (SCC) from a short DRX cycle to a long DRXcycle. The long DRX instruction message includes a message identity, acarrier identity, etc., and is generated at the MAC layer andtransmitted.

2. The base station instructs the terminal to switch a DRX operationcycle for another carrier (SCC) from a long DRX cycle to a short DRXcycle. The short DRX instruction message includes a message identity, acarrier identity, etc., and is generated at the MAC layer andtransmitted.

3. The base station instructs the terminal to stop an operation oftransmitting and receiving another carrier. The message is generated atthe RRC layer and transmitted.

4. The base station instructs the terminal to start an operation oftransmitting and receiving another carrier. The message is generated atthe RRC layer and transmitted.

FIG. 3 is a flowchart illustrating a process of switching a DRXoperation cycle for one or more carriers from a short DRX cycle to along DRX cycle in a DL of a mobile communication system using multiplecarriers according to example embodiments of the present invention, andFIG. 4 is a flowchart illustrating a process of switching a DRXoperation cycle for one or more carriers from a long DRX cycle to ashort DRX cycle in a DL of a mobile communication system using multiplecarriers according to other example embodiments of the presentinvention.

A process of switching a DRX operation cycle for one or more carriersfrom a short DRX cycle to a long DRX cycle in a DL of a mobilecommunication system using multiple carriers according to exampleembodiments of the present invention will be described in detail below.

Referring to FIG. 3 , first, a base station transmits a DL controlchannel, e.g., a PDCCH, to a terminal (operation 301). The DL controlchannel may include a CI (Carrier Indicator). By cross-carrierscheduling with a CI, a PDCCH of a serving cell can schedule resourcesof another serving cell. For example, using a CI, a PDCCH can allocatePDSCH or physical uplink shared channel (PUSCH) resources of one CCamong multiple carriers.

When the DL control channel is received, the terminal interprets the DLcontrol channel, receives a data channel, e.g., a PDSCH, of a PCC or SCCcorresponding to a carrier number indicated by the CI of the DL controlchannel, and demodulates data (operation 303). In other words, when a CIis included in the received control channel (“PDCCH with CI” of FIG. 2), the terminal receives a data channel of a SCC corresponding to acarrier number indicated by the CI, e.g., CC2 of FIG. 2 , to demodulatedata.

When the amount of data corresponding to a predetermined threshold valueor less is in a buffer for a predetermined time, the base stationtransmits a long DRX instruction message, which instructs the terminalto switch to long DRX, to the terminal (operation 305), and the terminalreceives the long DRX instruction message and switches to long DRX(operation 307). The long DRX instruction message can include a messageidentity, a carrier identity, and so on. A MAC message generated in theMAC layer can be used as the long DRX instruction message. The MACmessage can have a size of, for example, N bits (N is a natural number).

A process of switching a DRX operation cycle for one or more carriersfrom a long DRX cycle to a short DRX cycle in a DL of a mobilecommunication system using multiple carriers according to other exampleembodiments of the present invention will be described in detail below.

Referring to FIG. 4 , first, a base station transmits a DL controlchannel, e.g., a PDCCH, to a terminal (operation 401). The DL controlchannel may include a CI. By cross-carrier scheduling with a CI, a PDCCHof a serving cell can schedule resources of another serving cell. Forexample, using a CI, a PDCCH can allocate PDSCH or PUSCH resources ofone CC among multiple carriers.

When the DL control channel is received, the terminal interprets the DLcontrol channel, receives a data channel, e.g., a PDSCH, of a PCC or SCCcorresponding to a carrier number indicated by the CI of the DL controlchannel, and demodulates data (operation 403).

When the amount of data corresponding to a predetermined threshold valueor less is in a buffer for a predetermined time and then increases, thebase station transmits a short DRX instruction message, which instructsthe terminal to switch to short DRX, to the terminal (operation 405),and the terminal receives the short DRX instruction message and switchesto short DRX (operation 407). The Long DRX instruction message caninclude a message identity, a carrier identity, and so on. A MAC messagegenerated in the MAC layer can be used as the short DRX instructionmessage. The MAC message can have a size of, for example, N bits (N is anatural number).

In a multi-carrier environment using a CI, a DRX operation of one CC isinfluenced by receiving of a control channel of another CC. Thus, inexample embodiments of the present invention, when one carrier isinstructed to receive a data channel by another carrier, a terminalcarries out a procedure as if a control channel was received on acarrier of the terminal.

When a terminal receives a DL control channel, e.g., a PDCCH, in a longDRX period state in which the terminal receives a DL channel at longperiods, the terminal immediately switches to a short DRX period state,thereby receiving data at short periods. In this procedure, it isnecessary to reduce power consumption of the terminal caused when theterminal receives meaningless data and switches from a long DRX periodto a short DRX period.

In example embodiments of the present invention, when a terminalreceives a DL control channel, e.g., a PDCCH, in the long DRX periodstate but does not need to switch to the short DRX period state afterdemodulating the PDCCH or a PDSCH, the terminal stays in the long DRXperiod state. To be specific, after receiving a PDCCH, the terminaldemodulates the PDCCH and PDSCH to determine whether or not a type ofdata requires continuous data communication, and switches to a short DRXperiod only when continuous data communication is required.

Continuous data communication is not required in the following cases.

-   -   A base station allocates UL radio resources, but there is no        data in a buffer of a terminal.    -   A base station requests UL transmission to maintain UL        synchronization.    -   A base station requests UL transmission to retrieve location        information about a terminal.    -   A base station requests a DL channel state report.

When continuous data communication is not required as mentioned above,the terminal can continuously perform a long DRX period operation tominimize power consumption according to a procedure proposed in exampleembodiments of the present invention.

FIG. 5 is a flowchart illustrating a process for a base station toactivate a carrier of a terminal in a mobile communication system usingmultiple carriers, and FIG. 6 is a conceptual diagram illustrating aprocess for a base station to activate a carrier of a terminal in amobile communication system using multiple carriers. FIG. 7 illustratesa structure of a carrier activation message transmitted to a terminal bya base station.

A process for a base station to activate a carrier of a terminal in amobile communication system using multiple carriers will be described indetail below with reference to FIGS. 5 to 7 .

In an idle mode and an initial access mode for a base station, aterminal communicates with the base station using a single carrier,e.g., CC #1 for a DL and CC #1 for a UL as shown in FIG. 6 .

In the idle mode or the initial access mode in a mobile communicationsystem using multiple carriers, the base station transmits aconfiguration message to the terminal so that the terminal controls aplurality of CCs, thereby performing a configuration procedure(operation 501). The configuration message can be transmitted by thebase station using an RRC message. The RRC message can include thenumber of additional Scells and multi-SCC control information. Theconfiguration message can be the RRC message and can be used to add,modify, or release an Scell. The RRC message can be transmitted througha dedicated channel.

After receiving the configuration message, the terminal transmits aconfiguration response message as a receiving completion message to thebase station (operation 503). As a result, for example, theconfiguration procedure for DL CC #2 and CC #3 is complete asillustrated in FIG. 6 .

The terminal having completed the configuration procedure stores controlinformation for the multiple carriers included in the configurationmessage transmitted by the base station, but stands by to reduce powerconsumption of the terminal itself without performing communicationusing a carrier (e.g., DL CC #2 or DL CC #3 shown in FIG. 2 ) specifiedin the configuration message. To be specific, the terminal does notreceive a control channel of the configured carriers DL CC #2 and DL CC#3, and does not measure a channel state either.

After the configuration procedure is complete, the base stationtransmits a carrier activation message to the terminal, therebyperforming a carrier activation procedure (operation 505). The terminalreceives the carrier activation message to activate the correspondingcarrier (operation 507). For example, DL CC #2 and DL CC #3 areactivated as shown in FIG. 6 . After receiving the carrier activationmessage, the terminal transmits an ACK/NACK to the base station(operation 509). The ACK/NACK may be sent immediately after the terminalreceives the carrier activation message, or after the terminal receivesthe carrier activation message and then activates the correspondingcarrier (operation 507). When the activation procedure is complete, theterminal actually uses the activated carrier for communication with thebase station. Through the above-described operations, a DL multi-carrieractivation procedure is carried out.

A carrier activation message according to example embodiments of thepresent invention is transmitted through a data channel 720 transmittedto a terminal by a base station, and can be a MAC control message asshown in FIG. 7 . Referring to FIG. 7 , the MAC control message includesa control channel 710 and a data channel 720, and the data channel 720may consist of a data channel header 721, a carrier activation message723, and traffic data 727. In other words, the carrier activationmessage 723 can be included in the data channel 720 of the MAC controlmessage.

The carrier activation message 723 can include an activation ordeactivation carrier identity. The carrier activation message 723 mayfurther include an activation or deactivation identity. The carrieractivation message 723 may be transmitted along with traffic data, whichis transmitted to the terminal by the base station, by a piggybackmechanism. A plurality of carrier activation messages may be stored inone data channel and transmitted.

When the carrier activation procedure is complete and a plurality ofcarriers are activated, all the activated carriers perform the powerconsumption reducing operation through the DRX procedure illustrated inFIGS. 1 and 2 , and the terminal communicates with the base stationusing all the activated carriers. The activated carriers can be switchedto the standby state when the base station transmits a carrierdeactivation message to the terminal. The carrier deactivation messagecan have the same format as the carrier activation message. In otherwords, the carrier deactivation message can be included in a datachannel of a MAC control message and transmitted, and can include adeactivation carrier identity.

A UL carrier activation procedure according to example embodiments ofthe present invention can be carried out in the same manner as theabove-described DL carrier activation procedure. In other words, thebase station transmits a configuration message and a carrier activationmessage to the terminal, so that the UL carrier activation procedure canbe carried out.

During the UL carrier activation procedure, the base station can includea transmission cycle of a physical control channel (e.g., a PUCCH orsounding reference symbol (SRS)) or information for separatelyindicating a transmission start in the configuration message andtransmit the configuration message to the terminal. Alternatively, thetransmission cycle of a physical control channel (e.g., a PUCCH or SRS)or the information for separately indicating a transmission start may beincluded in the carrier activation message and transmitted to theterminal. For example, a transmission cycle of a PUCCH, which is a ULcontrol channel, or SRS may be included in the carrier activationmessage and transmitted to the terminal.

Using a format similar to that of the carrier activation message of FIG.6 , the configuration message for activating a UL carrier may betransmitted along with traffic data, which is transmitted to theterminal by the base station, by a piggyback mechanism. Also, aplurality of carrier activation messages may be stored in one datachannel and transmitted.

Alternatively, a UL carrier activation procedure can be controlled inconnection with DL carrier activation. When UL control is performed inconnection with DL control, the number of control message transmissionsbetween the base station and the terminal and the amount of control dataare reduced.

A UL carrier configuration procedure according to other exampleembodiments of the present invention can be carried out in connectionwith a DL carrier configuration procedure at the same time.

The UL carrier activation procedure carried out after the DL carrierconfiguration procedure can be simultaneously performed with a DLactivation procedure. To be specific, mapping information about a ULcarrier interoperating with a DL carrier can be included in the DLconfiguration message of operation 501 and transmitted to the terminal.The carrier mapping information can indicate that DL CC #2 interoperateswith UL CC #2 as illustrated in FIG. 6 and hybrid automatic repeatrequest (HARQ) ACK/NACK transmission resources operate in connectionwith each other, and also indicate that DL CC #3 interoperates with ULCC #3 and HARQ ACK/NACK transmission resources operate in connectionwith each other. Further, the carrier mapping information can indicatethat a PDCCH indicating permission for transmission of a UL data channeloperates in connection with resource information about the UL datachannel (PUSCH). Thus, the base station includes all mapping informationin the configuration message, transfers the configuration message to theterminal in advance, and thus can implicitly start UL carrier activationas soon as a DL activation message is received by the terminal withouttransmitting a UL carrier activation message to the terminal (operation511 of FIG. 5 ). For example, as illustrated in FIG. 6 , after thecarrier activation message of operation 505 is received, the terminalcan activate the corresponding carrier (DL CC #2 and DL CC #3) andimplicitly activate UL CC #2 and UL CC #3 at the same time.

When a DL carrier is instructed to be activated, the terminal canactivate a UL carrier mapped to the DL carrier and use the UL carrierfor communication. Thus, when the base station makes an instruction forUL data transmission, an activated UL carrier can be used when theterminal transmits data to the base station, and a UL control channel(e.g., a PUCCH or SRS) can be transmitted according to a set condition.An activated UL carrier can be deactivated as soon as a deactivationprocedure of a previously mapped DL carrier is complete.

A UL carrier whose activation procedure is complete requires the basestation and the terminal to operate in synchronization with each other.Thus, the base station and the terminal manage a UL synchronizationtimer, thereby managing synchronization. The base station sets the timerat a point in time that synchronization of the terminal is maintained tostore the maximum synchronization maintenance time. After this, when avalue of the timer is due at a point in time that an activation messageis received and synchronization is lost, the base station restoressynchronization of the carrier using a random access procedure and thenperforms an activation operation. When the random access procedure issuccessful, the base station and the terminal reset the timer to themaximum synchronization maintenance time, and carry out asynchronization maintenance procedure using a data channel in a UL datatransceiving state.

Different numbers of DL carriers and UL carriers may be mapped to eachother. Even when different numbers of DL carriers and UL carriers aremapped to each other, a UL carrier configuration procedure can becarried out in connection with a DL carrier configuration procedure atthe same time. Even when different numbers of DL carriers and ULcarriers are mapped to each other, mapping information is included in aconfiguration message and transmitted to the terminal in advance by thebase station, so that UL carrier activation can be implicitly started assoon as a DL activation message is received by the terminal withouttransmitting a UL carrier activation message to the terminal.

While the example embodiments of the present invention and theiradvantages have been described in detail, it should be understood thatvarious changes, substitutions and alterations may be made hereinwithout departing from the scope of the invention.

What is claimed is:
 1. A communication method performed by a userequipment (UE), the method comprising: receiving a first message relatedto a first discontinuous reception cycle from a base station; monitoringa physical downlink control channel (PDCCH) on a first component carrierbased on the first discontinuous reception cycle; receiving firstcontrol information through the PDCCH on the first component carrier;receiving a second message related to a second discontinuous receptioncycle from the base station based on the first control information;monitoring the PDCCH on the first component carrier based on the seconddiscontinuous reception cycle; receiving second control informationthrough the PDCCH on the first component carrier, wherein the secondcontrol information identifies a second component carrier; and receivingthrough a physical downlink shared channel (PDSCH) on the secondcomponent carrier based on the second control information, wherein thesecond discontinuous reception cycle is different from the firstdiscontinuous reception cycle.
 2. The method of claim 1, wherein: thefirst message also indicates a first period during which the UE monitorsthe PDCCH and a second period during which the UE does not monitor thePDCCH, wherein the first discontinuous reception cycle comprises thefirst period and the second period.
 3. The method of claim 1, whereinthe second message is received through a physical downlink sharedchannel (PDSCH) of the first component carrier.
 4. The method of claim1, wherein the first and second messages are radio resource control(RRC) messages.
 5. The method of claim 1, wherein the second controlinformation comprises a carrier indicator (Cl) of the second componentcarrier.
 6. The method of claim 1, wherein the second discontinuousreception cycle is longer than the first discontinuous reception cycle.7. A user equipment (UE), comprising: a circuitry, which is configuredto: cause the UE to receive a first message related to a firstdiscontinuous reception cycle from a base station; cause the UE tomonitor a physical downlink control channel (PDCCH) on a first componentcarrier based on the first discontinuous reception cycle; cause the UEto receive first control information through the PDCCH on the firstcomponent carrier; cause the UE to receive a second message related to asecond discontinuous reception cycle from the base station based on thefirst control information; cause the UE to monitor the PDCCH on thefirst component carrier based on the second discontinuous receptioncycle; cause the UE to receive second control information through thePDCCH on the first component carrier, wherein the second controlinformation identifies a second component carrier; and cause the UE toreceive data through a physical downlink shared channel (PDSCH) on thesecond component carrier based on the second control information,wherein the second discontinuous reception cycle is different from thefirst discontinuous reception cycle.
 8. The user equipment of claim 7,wherein: the first message also indicates a first period during whichthe UE monitors the PDCCH and a second period during which the UE doesnot monitor the PDCCH, wherein the first discontinuous reception cyclecomprises the first period and the second period.
 9. The user equipmentof claim 7, wherein the second message is received through a physicaldownlink shared channel (PDSCH) of the first component carrier.
 10. Theuser equipment of claim 7, wherein the first and second messages areradio resource control (RRC) messages.
 11. The user equipment of claim7, wherein the second control information comprises a carrier indicator(Cl) of the second component carrier.
 12. The user equipment of claim 7,wherein the second discontinuous reception cycle is longer than thefirst discontinuous reception cycle.
 13. A communication device for auser equipment (UE), the communication device comprising: a circuitry,which is configured to: cause the UE to receive a first message relatedto a first discontinuous reception cycle from a base station; cause theUE to monitor a physical downlink control channel (PDCCH) on a firstcomponent carrier based on the first discontinuous reception cycle;cause the UE to receive first control information through the PDCCH onthe first component carrier; cause the UE to receive a second messagerelated to a second discontinuous reception cycle from the base stationbased on the first control information; cause the UE to monitor thePDCCH on the first component carrier based on the second discontinuousreception cycle; cause the UE to receive second control informationthrough the PDCCH on the first component carrier, wherein the secondcontrol information identifies a second component carrier; and cause theUE to receive data through a physical downlink shared channel (PDSCH) onthe second component carrier based on the second control information,wherein the second discontinuous reception cycle is different from thefirst discontinuous reception cycle.
 14. The communication device ofclaim 13, wherein: the first message also indicates a first periodduring which the UE monitors the PDCCH and a second period during whichthe UE does not monitor the PDCCH, wherein the first discontinuousreception cycle comprises the first period and the second period. 15.The communication device of claim 13, wherein the second message isthrough a physical downlink shared channel (PDSCH) of the firstcomponent carrier.
 16. The communication device of claim 13, wherein thefirst and second messages are radio resource control (RRC) messages. 17.The communication device of claim 13, wherein the second controlinformation comprises a carrier indicator (CI) of the second componentcarrier.
 18. The communication device of claim 13, wherein the seconddiscontinuous reception cycle is longer than the first discontinuousreception cycle.